Signal line and circuit substrate

ABSTRACT

A signal line is a linear conductor provided within a laminated body. A first ground conductor is provided on a positive direction side in a z axis direction within the laminated body, compared with the signal line, and overlaps with the signal line in a planar view seen from the z axis direction. A second ground conductor is provided on a negative direction side in the z axis direction within the laminated body, compared with the signal line, and overlaps with the signal line in the planar view seen from the z axis direction. Via hole conductors connect the ground conductors to each other. In the first ground conductor, a plurality of opening portions are arranged along the signal line in the planar view seen from the z axis direction. The via hole conductors are provided between the opening portions adjacent to one another, in an x axis direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a signal line and the circuit substratethereof, and, more specifically, relates to a signal line that iscapable of being easily inflected and reducing unnecessary radiation,and a circuit substrate thereof.

2. Description of the Related Art

As a signal line of the related art, for example, a flexible substratedescribed in Japanese Unexamined Patent Application Publication No.2007-123740 is known. FIGS. 5A and 5B are cross-section structurediagrams of a flexible substrate 500 described in Japanese UnexaminedPatent Application Publication No. 2007-123740.

A cross-section structure illustrated in FIG. 5A and a cross-sectionstructure illustrated in FIG. 5B are alternately disposed, and hence theflexible substrate 500 is configured. More specifically, the flexiblesubstrate 500 includes insulation layers 502 a to 502 d, a signal line504 and ground layers 506 a and 506 b. Insulation layers 502 a to 502 dare sheets including flexible material and laminated. The signal line504 is provided on the insulation layer 502 c, and extends parallel tothe vertical direction of the plane of paper of FIG. 5A.

As illustrated in FIG. 5A, the ground layer 506 a is provided on theinsulation layer 502 b, and located above the signal line 504 in alamination direction. As illustrated in FIG. 5A, the ground layer 506 bis provided on the insulation layer 502 d, and located below the signalline 504 in the lamination direction. In this way, in the flexiblesubstrate 500, in the cross-section structure diagram illustrated inFIG. 5A, the ground layers 506 a and 506 b overlap with the signal line504 in the lamination direction. In this regard, however, in theflexible substrate 500, in the cross-section structure diagramillustrated in FIG. 5B, the ground layers 506 a and 506 b do not overlapwith the signal line 504 in the lamination direction. Namely, openingportions 508 a and 508 b are provided in the ground layers 506 a and 506b, respectively.

Such a flexible substrate 500 as described above is easy to inflect anduse, as described below. More specifically, since the ground layers 506a and 506 b are configured using metal foil or the like, it is hard forthe ground layers 506 a and 506 b to expand and contract compared withthe insulation layers 502 a to 502 d. Therefore, as illustrated in FIG.5B, in the flexible substrate 500, the opening portions 508 a and 508 bare provided in the ground layers 506 a and 506 b. Accordingly, in aportion illustrated in FIG. 5B, since the widths of the ground layers506 a and 506 b become small, it is easy for the ground layers 506 a and506 b to expand and contract. As a result, it is possible to easily bendthe flexible substrate 500.

However, the flexible substrate 500 has a problem that unnecessaryradiation from the signal line 504 occurs. More specifically, theopening portions 508 a and 508 b are provided in the ground layers 506 aand 506 b. Therefore, in a planar view seen from a lamination direction,the signal line 504 is exposed through the opening portions 508 a and508 b. As a result, unnecessary radiation that is fundamentally absorbedby the ground layers 506 a and 506 b leaks to the outside of theflexible substrate 500 through the opening portions 508 a and 508 b.

SUMMARY OF THE INVENTION

Therefore, preferred embodiments of the present invention provide asignal line and a circuit substrate, which are capable of being easilyinflected and reducing unnecessary radiation.

A signal line according to a first preferred embodiment of the presentinvention includes a laminated body including a plurality of insulatorlayers that include flexible material and are laminated; a linear signalline provided within the laminated body; a first ground conductorlocated above the linear signal line in a lamination direction withinthe laminated body and overlapping with the linear signal line in aplanar view seen from the lamination direction; a second groundconductor located below the linear signal line in the laminationdirection within the laminated body and overlapping with the linearsignal line in the planar view seen from the lamination direction; and avia hole conductor connecting the first ground conductor and the secondground conductor to each other, wherein in the first ground conductor, aplurality of first opening portions are arranged along the linear signalline in the planar view seen from the lamination direction, and in theplanar view seen from the lamination direction, the via hole conductoris located between the first opening portions adjacent to each other, ina direction in which the linear signal line extends.

A circuit substrate according to a second preferred embodiment of thepresent invention includes a main body including a plurality ofinsulator layers that include flexible material and are laminated andincluding a first circuit portion, a second circuit portion, and asignal line portion; a linear signal line provided within the signalline portion; a first ground conductor located above the linear signalline in a lamination direction within the signal line portion andoverlapping with the linear signal line in a planar view seen from thelamination direction; a second ground conductor located below the signalline in the lamination direction within the signal line portion andoverlapping with the linear signal line in the planar view seen from thelamination direction; and a via hole conductor connecting the firstground conductor and the second ground conductor to each other, whereinin the first ground conductor, a plurality of first opening portions arearranged along the linear signal line in the planar view seen from thelamination direction, in the planar view seen from the laminationdirection, the via hole conductor is provided between the first openingportions adjacent to each other, in a direction in which the linearsignal line extends, and the first circuit portion and the secondcircuit portion include a first circuit and a second circuit,respectively, the first circuit and the second circuit being connectedto the linear signal line, the first ground conductor, and the secondground conductor.

According to various preferred embodiments of the present invention, itis possible to easily inflect a signal line and a circuit substrate andit is also possible to reduce unnecessary radiation.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external appearance perspective view of a signal lineaccording to a preferred embodiment of the present invention.

FIGS. 2A-2D are exploded views of the signal line in FIG. 1.

FIGS. 3A-3D are exploded views of a signal line according to an exampleof a modification of a preferred embodiment of the present invention.

FIG. 4 is an exploded perspective view of a circuit substrate accordingto a second preferred embodiment of the present invention.

FIGS. 5A and 5B are cross-section structure diagrams of a flexiblesubstrate described in Japanese Unexamined Patent ApplicationPublication No. 2007-123740.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a signal line and a circuit substrate according topreferred embodiments of the present invention will be described withreference to drawings.

First Preferred Embodiment

Hereinafter, the configuration of a signal line according to a firstpreferred embodiment of the present invention will be described withreference to drawings. FIG. 1 is an external appearance perspective viewof a signal line 10 a, 10 b according to a preferred embodiment of thepresent invention. FIGS. 2A-2D are exploded views of the signal line 10a in FIG. 1. In FIG. 1 and FIGS. 2A-2D, the lamination direction of thesignal line 10 a is defined as a z axis direction. In addition, thelongitudinal direction of the signal line 10 a is defined as an x axisdirection, and a direction perpendicular to the x axis direction and thez axis direction is defined as a y axis direction, for example.

For example, the signal line 10 a connects two circuit substrates toeach other in an electronic device such as a mobile phone or the like.As illustrated in FIG. 1 and FIGS. 2A-2D, the signal line 10 a includesa laminated body 12, external terminals 14 (14 a to 14 f), groundconductors 30 and 34, a linear signal line 32, and via hole conductorsb1 to b16 and B1 to B36.

As illustrated in FIG. 1, the laminated body 12 includes a signal lineportion 16 and connector portions 18 and 20. The signal line portion 16extends in the x axis direction, and includes the linear signal line 32and the ground conductors 30 and 34. The signal line portion 16preferably is configured so as to be able to be bent into a U shape. Theconnector portions 18 and 20 are provided at both ends of the signalline portion 16 in the x axis direction, and connected to the connectorsof the circuit substrates not illustrated. Insulation sheets (insulatorlayers) 22 (22 a to 22 d) illustrated in FIGS. 2A-2D are laminated fromthe positive direction side of the z axis direction to the negativedirection side thereof in this order, thereby configuring the laminatedbody 12.

The insulation sheet 22 is preferably made of thermoplastic resin suchas liquid crystalline polymer having flexibility, or the like. Asillustrated in FIGS. 2A-2D, the insulation sheets 22 a to 22 dpreferably include signal line portions 24 a to 24 d, connector portions26 a to 26 d, and connector portions 28 a to 28 d, respectively. Thesignal line portion 24 configures the signal line portion 16 of thelaminated body 12, and the connector portions 26 and 28 configure theconnector portions 18 and 20 of the laminated body 12, respectively. Inaddition, hereinafter, a main surface on a positive direction side inthe z axis direction of the insulation sheet 22 is referred to as afront surface, and a main surface on a negative direction side in the zaxis direction of the insulation sheet 22 is referred to as a backsurface.

As illustrated in FIGS. 2A-2D, the external terminals 14 a to 14 c arearranged so as to define a line in the y axis direction on the frontsurface of the connector portion 26 a. When the connector portion 18 isinserted into the connector of the circuit substrate, the externalterminals 14 a to 14 c are in contact with terminals within theconnector. Specifically, the external terminals 14 a and 14 c are incontact with ground terminals within the connector, and the externalterminal 14 b is in contact with a signal terminal within the connector.Accordingly, a ground potential is applied to the external terminals 14a and 14 c, and a high-frequency signal (for example, about 2 GHz) isapplied to the external terminal 14 b.

As illustrated in FIGS. 2A-2D, the external terminals 14 d to 14 f arearranged so as to define a line in the y axis direction on the frontsurface of the connector portion 28 a. When the connector portion 20 isinserted into the connector of the circuit substrate, the externalterminals 14 d to 14 f are in contact with terminals within theconnector. Specifically, the external terminals 14 d and 14 f are incontact with ground terminals within the connector, and the externalterminal 14 e is in contact with a signal terminal within the connector.Accordingly, a ground potential is applied to the external terminals 14d and 14 f, and a high-frequency signal (for example, about 2 GHz) isapplied to the external terminal 14 e.

As illustrated in FIGS. 2A-2D, the linear signal line preferably is alinear conductor provided within the laminated body 12, and preferablyis provided on the front surface of the insulation sheet 22 c. Thelinear signal line 32 extends in the x axis direction on the frontsurface of the insulation sheet 24 c. In addition, both ends of thelinear signal line 32 are located at the connector portions 26 c and 28c, respectively.

As illustrated in FIGS. 2A-2D, the ground conductor 30 is provided on apositive direction side in the z axis direction within the laminatedbody 12, compared with the linear signal line 32, and more specifically,is provided on the front surface of the insulation sheet 22 b. Theground conductor 30 extends in the x axis direction on the front surfaceof the signal line portion 24 b. One end of the ground conductor 30 isarranged such that the end thereof branches into two portions in theconnector portion 26 b, and the other end of the ground conductor 30 isarranged such that the end thereof branches into two portions in theconnector portion 28 b. Furthermore, as illustrated in FIGS. 2A-2D, theground conductor 30 overlaps with the signal line 32 in a planar viewseen from the z axis direction.

In addition, as illustrated in FIGS. 2A-2D, in the ground conductor 30,a plurality of slit-shaped opening portions O1 to O8 in which noconductor is provided are arranged along the linear signal line 32 inthe planar view seen from the z axis direction. In the present preferredembodiment, the opening portions O1 to O8 overlap with the linear signalline 32 in the planar view seen from the z axis direction. Furthermore,the opening portions O1 to O8 preferably have rectangular orsubstantially rectangular shapes whose longitudinal directionscorrespond to the y axis direction, and define a line in the x axisdirection at regular intervals, for example. In addition, the openingsO1 to O8 are arranged so as not to divide the ground conductor 30. Morespecifically, the conductor of the ground conductor 30 exists on thepositive direction side and the negative direction side of the openingsO1 to O8 in the y axis direction. Accordingly, the ground conductor 30preferably has a ladder shape. As described above, the openings O1 to O8are provided in the ground conductor 30, and hence, as illustrated inFIGS. 2A-2D, in the ground conductor 30, a relatively thick portion anda relatively thin portion are provided in width in the y axis direction.

As illustrated in FIGS. 2A-2D, the ground conductor 34 is provided on anegative direction side in the z axis direction within the laminatedbody 12, compared with the linear signal line 32, and more specifically,is provided on the front surface of the insulation sheet 22 d. Theground conductor 34 extends in the x axis direction on the front surfaceof the signal line portion 24 d. One end of the ground conductor 34 isarranged such that the end thereof branches into two portions in theconnector portion 26 d, and the other end of the ground conductor 34 isarranged such that the end thereof branches into two portions in theconnector portion 28 d. Furthermore, as illustrated in FIGS. 2A-2D, theground conductor 34 overlaps with the linear signal line 32 in theplanar view seen from the z axis direction.

In addition, in the ground conductor 34, a plurality of slit-shapedopening portions O11 to O18 in which no conductor is provided arearranged along the linear signal line 32 in the planar view seen fromthe z axis direction. In the present preferred embodiment, the openingportions O11 to O18 overlap with the linear signal line 32 in the planarview seen from the z axis direction. In addition, in the planar viewseen from the z axis direction, the opening portions O11 to O18 overlapwith the opening portions O1 to O8, respectively, in a state in whichthe opening portions O11 to O18 coincide with the opening portions O1 toO8, respectively. More specifically, in the same way as the openingportions O1 to O8, the opening portions O11 to O18 preferably haverectangular or substantially rectangular shapes whose longitudinaldirections correspond to the y axis direction, and define a line in thex axis direction at regular intervals. In addition, in the same way asthe opening portions O1 to O8, the opening portions O11 to O18 arearranged so as not to divide the ground conductor 34. More specifically,the conductor of the ground conductor 34 exists on the positivedirection side and the negative direction side of the openings O11 toO18 in the y axis direction. Accordingly, the ground conductor 34preferably has a ladder shape. As described above, the openings O11 toO18 are provided in the ground conductor 34, and hence, as illustratedin FIGS. 2A-2D, in the ground conductor 34, a relatively thick portionand a relatively thin portion are provided in the width thereofextending in the y axis direction.

As illustrated in FIGS. 2A-2D, the via hole conductors b1 and b3 areprovided so as to penetrate through the connector portion 26 a in the zaxis direction, and connect the external terminals 14 a and 14 c to theground conductor 30, respectively. As illustrated in FIGS. 2A-2D, thevia hole conductor b2 is provided so as to penetrate through theconnector portion 26 a in the z axis direction, and is connected to theexternal terminal 14 b.

As illustrated in FIGS. 2A-2D, each of the via hole conductors b7 and b9is provided so as to penetrate through the connector portion 26 b in thez axis direction, and is connected to the ground conductor 30. Asillustrated in FIGS. 2A-2D, the via hole conductor b8 is provided so asto penetrate through the connector portion 26 b in the z axis direction,and connects the via hole conductor b2 and the linear signal line 32 toeach other.

As illustrated in FIGS. 2A-2D, the via hole conductors b13 and b14 areprovided so as to penetrate through the connector portion 26 c in the zaxis direction, and connect the via hole conductors b7 and b9 to theground conductor 34, respectively. Accordingly, the external terminal 14a is connected to the ground conductors 30 and 34 through the via holeconductors b1, b7, and b13, and the external terminal 14 c is connectedto the ground conductors 30 and 34 through the via hole conductors b3,b9, and b14. In addition, the external terminal 14 b and the linearsignal line 32 are connected to each other through the via holeconductors b2 and b8.

As illustrated in FIGS. 2A-2D, the via hole conductors b4 and b6 areprovided so as to penetrate through the connector portion 28 a in the zaxis direction, and connect the external terminals 14 d and 14 f to theground conductor 30, respectively. As illustrated in FIGS. 2A-2D, thevia hole conductor b5 is provided so as to penetrate through theconnector portion 28 a in the z axis direction, and is connected to theexternal terminal 14 e.

As illustrated in FIGS. 2A-2D, each of the via hole conductors b10 andb12 is provided so as to penetrate through the connector portion 28 b inthe z axis direction, and is connected to the ground conductor 30. Asillustrated in FIGS. 2A-2D, the via hole conductor b11 is provided so asto penetrate through the connector portion 28 b in the z axis direction,and connects the via hole conductor b5 and the linear signal line 32 toeach other.

As illustrated in FIGS. 2A-2D, the via hole conductors b15 and b16 areprovided so as to penetrate through the connector portion 28 c in the zaxis direction, and connect the via hole conductors b10 and b12 to theground conductor 34, respectively. Accordingly, the external terminal 14d is connected to the ground conductors 30 and 34 through the via holeconductors b4, b10, and b15, and the external terminal 14 f is connectedto the ground conductors 30 and 34 through the via hole conductors b6,b12, and b16. In addition, the external terminal 14 e and the linearsignal line 32 are connected to each other through the via holeconductors b5 and b11.

As illustrated in FIGS. 2A-2D, the via hole conductors B1 to B18 and thevia hole conductors B19 to B36 are provided so as to penetrate throughthe signal line portions 24 b and 24 c in the z axis direction,respectively, and connect the ground conductor 30 and the groundconductor 34 to each other. Furthermore, in the planar view seen fromthe z axis direction, the via hole conductors B1 to B18 are providedbetween the opening portions O1 to O8 adjacent to one another, in adirection (specifically, the x axis direction) in which the signal line32 extends. In additions, the via hole conductors B1, B3, B5, B7, B9,B11, B13, B15, and B17 are arranged so as to lie on a straight line inthe x axis direction with being equally spaced. In addition, on anegative direction side in the y axis direction, compared with the viahole conductors B1, B3, B5, B7, B9, B11, B13, B15, and B17, the via holeconductors B2, B4, B6, B8, B10, B12, B14, B16, and B18 are arranged soas to lie on a straight line in the x axis direction with being equallyspaced.

Furthermore, in the present preferred embodiment, the via holeconductors B3 to B16 are provided on perpendicular bisectors withrespect to the centers of the opening portions O1 to O8 adjacent to oneanother. Hereinafter, the via hole conductors B3 and B4 will bedescribed as an example. As illustrated in FIGS. 2A-2D, the via holeconductors B3 and B4 are provided between the opening portion O1 and theopening portion O2. Hereinafter, the points of intersection between thediagonal lines of the opening portions O1 and O2 are referred to as thecenters P1 and P2 of the opening portions O1 and O2. In addition, theperpendicular bisector of the centers P1 and P2 is referred to as astraight line L1. The via hole conductor B3 is located on the straightline L1, and is provided so as to overlap with end portions on thepositive direction sides of the openings O1 to O8 in the y axisdirection in the planar view seen from the x axis direction. Inaddition, the via hole conductor B4 is located on the straight line L1,and is arranged so as to overlap with end portions on the negativedirection sides of the openings O1 to O8 in the y axis direction in theplanar view seen from the x axis direction.

The via hole conductors B19 to B36 are arranged in the signal lineportion 24 c so as to overlap with the via hole conductors B1 to B18,respectively, in the planar view seen from the z axis direction.Accordingly, the via hole conductors B19 to B36 are connected to the viahole conductors B1 to B18, respectively.

The insulation sheets 22 a to 22 d having the above-mentionedconfigurations are laminated, and hence the ground conductors 30 and 34and the linear signal line 32 define a stripline structure. Morespecifically, as illustrated in FIGS. 2A-2D, the linear signal line 32is sandwiched in between the ground conductor 30 and the groundconductor 34 in the z axis direction, and is housed within a region inwhich the ground conductors 30 and 34 are provided, in the planar viewseen from the z axis direction. Furthermore, the ground conductor 30 andthe ground conductor 34 are connected to each other through the via holeconductors B1 to B36.

The signal line 10 a having the above-mentioned configuration is used ina state in which the signal line 10 a is inflected. Namely, in theplanar view seen from the y axis direction, the signal line 10 a isinflected so as to form a U shape protruding toward one of a positivedirection side and a negative direction side in the z axis direction.

Hereinafter, a manufacturing method for the signal line 10 a will bedescribed with reference to FIGS. 2A-2D. While, hereinafter, a case inwhich one signal line 10 a is manufactured will be described as anexample, actually, large-sized insulation sheets are laminated and cut,thereby simultaneously manufacturing a plurality of the signal lines 10a.

First, the insulation sheet 22 is prepared where copper foil is formedon the entire surface of the front surface. For example, the frontsurface of the copper foil of the insulation sheet 22 is plated withzinc for antirust effect, thereby being smoothed.

Next, the external terminal 14 illustrated in FIGS. 2A-2D is formed onthe front surface of the insulation sheet 22 a through aphotolithography process. Specifically, on the copper foil of theinsulation sheet 22 a, resist having the same shape as the externalterminal 14 illustrated in FIGS. 2A-2D is printed. In addition, thecopper foil is subjected to etching processing, thereby removing thecopper foil of a portion not covered with the resist. After that, theresist is removed. Accordingly, such an external terminal 14 asillustrated in FIGS. 2A-2D is formed on the front surface of theinsulation sheet 22 a.

Next, the ground conductor 30 illustrated in FIGS. 2A-2D is formed onthe front surface of the insulation sheet 22 b through aphotolithography process. In addition, the linear signal line 32illustrated in FIGS. 2A-2D is formed on the front surface of theinsulation sheet 22 c through a photolithography process. In addition,the ground conductor 34 illustrated in FIGS. 2A-2D is formed on thefront surface of the insulation sheet 22 d through a photolithographyprocess. In addition, since these photolithography processes are thesame as the photolithography process performed when the externalterminal 14 is formed, the descriptions thereof will be omitted. Owingto the above-mentioned processes, the ground conductors 30 and 34 adhereto the front surfaces of the insulation sheets 22 b and 22 d, and thelinear signal line 32 adheres to the front surface of the insulationsheet 22 c.

Next, positions at which the via hole conductors b1 to b16 and B1 to B36of the insulation sheets 22 a to 22 c are to be formed are irradiatedwith a laser beam from a back surface side, thereby forming via holes.After that, via holes formed in the insulation sheets 22 a to 22 c arefilled with conductive paste whose main component is copper, there byforming the via hole conductors b1 to b16 and B1 to B36 illustrated inFIGS. 2A-2D.

Next, the insulation sheets 22 a to 22 d are stacked from a positivedirection side in the z axis direction to a negative direction sidetherein in this order so that the ground conductor 30, the linear signalline 32, and the ground conductor 34 define a stripline structure. Inaddition, by applying pressure on the insulation sheets 22 a to 22 dfrom the positive direction side in the z axis direction and thenegative direction side therein, the insulation sheets 22 a to 22 d arefixed. Accordingly, the signal line 10 a illustrated in FIG. 1 isobtained.

According to such a signal line 10 a as described above, it is possibleto easily bend the signal line 10 a into a U shape, as described below.Since the ground conductors 30 and 34 are configured using metal foil orthe like, it is hard for the ground conductors 30 and 34 to expand andcontract compared with the insulation layers 22 a to 22 d. Therefore, inthe signal line 10 a, as illustrated in FIGS. 2A-2D, the openingportions O1 to O8 and O11 to O18 are provided in the ground conductors30 and 34. Accordingly, the strengths of the ground conductors 30 and 34in portions in which the opening portions O1 to O8 and O11 to O18 areprovided become lower than the strengths of the ground conductors 30 and34 in other portions. Specifically, the ground conductors 30 and 34easily expand and contract in the x axis direction in portions on apositive direction side in the y axis direction and a negative directionside therein in portions in which the opening portions O1 to O8 and O11to O18 are provided compared with other portions. As a result, itbecomes possible to easily bend the signal line 10 a. In addition, sincethe opening portions O1 to O8 and O11 to O18 are provided in both of theground conductors 30 and 34 in the signal line 10 a, the signal line 10a may be inflected so as to form a U shape protruding toward a positivedirection side in the z axis direction in the planar view seen from they axis direction, and furthermore, may also be inflected so as to form aU shape protruding toward a negative direction side in the z axisdirection.

Furthermore, according to the signal line 10 a, it is possible to reduceunnecessary radiation as described below. As illustrated in FIGS. 2A-2D,in the signal line 10 a, the signal line 32 is exposed through theopenings O1 to O8 and O11 to O18, in the planar view seen from the zaxis direction. Therefore, it may be possible that unnecessary radiationfrom the signal line leaks to the outside of the signal line 10 athrough the openings O1 to O8 and O11 to O18.

However, in the signal line 10 a, the ground conductors 30 and 34 areconnected using the via hole conductors B1 to B36. Accordingly, a groundpotential becomes more securely and reliably applied to the groundconductors 30 and 34. Therefore, even if the openings O1 to O8 and O11to O18 exist, the unnecessary radiation from the signal line 32 isreadily absorbed by the ground conductors 30 and 34. As a result, theunnecessary radiation from the linear signal line 32, which leaks to theoutside of the signal line 10 a, is reduced.

In addition, since the via hole conductors B1 to B36 is configured usingmetal, it is difficult for the via hole conductors B1 to B36 to bedeformed compared with the insulation sheets 22 a to 22 d. Therefore,there is a possibility that the via hole conductors B1 to B36 preventthe signal line 10 a from being easily inflected. However, for thereason described below, even if the via hole conductors B1 to B36 areprovided, it is possible for the signal line 10 a to become easilyinflected.

More specifically, for example, when the signal line 10 a is inflectedso as to have a U shape protruding toward a positive direction side inthe z axis direction, the ground conductor 30 relatively largelystretches in the x axis direction in portions on positive directionsides and negative direction sides in the y axis direction of theportions in which the opening portions O1 to O8 are provided. On theother hand, the ground conductor 30 only relatively slightly stretchesin portions sandwiched in between the opening portions O1 to O8.Therefore, the via hole conductors B1 to B36 are provided between theopening portions O1 to O8 adjacent to one another in the x axisdirection. More specifically, the via hole conductors B1 to B36 areprovided in portions sandwiched in between the opening portions O1 toO8. Accordingly, the via hole conductors B1 to B36 do not prevent theportions on the positive direction sides and the negative directionsides in the y axis direction of the portions in which the openingportions O1 to O8 are provided from largely stretching. As a result, itis possible for the signal line 10 a to become easily inflected. Inaddition, since the physical phenomenon of a case in which the signalline 10 a is inflected so as to have a U shape protruding toward anegative direction side in the z axis direction is basically the same asthe physical phenomenon of a case in which the signal line 10 a isinflected so as to form a U shape protruding toward a positive directionside in the z axis direction, the description thereof will be omitted.

Furthermore, as illustrated in FIGS. 2A-2D, the via hole conductors B3to B16 are provided on the perpendicular bisectors with respect to thecenters of the opening portions O1 to O8 adjacent to one another.Accordingly, for the reason described below, it is possible to easilyinflect the signal line 10 a. More specifically, the portions on thepositive direction sides and the negative direction sides in the y axisdirection of the portions in which the opening portions O1 to O8 areprovided are portions most largely stretching when the signal line 10 ais inflected. On the other hand, in the portions sandwiched in betweenthe opening portions O1 to O8, the perpendicular bisectors with respectto the centers of the opening portions O1 to O8 adjacent to one anotherare located, in the x axis direction, furthest away from the portions onthe positive direction sides and the negative direction sides in the yaxis direction of the portions in which the opening portions O1 to O8are provided. Therefore, the via hole conductors B3 to B16 are disposedso as to be located away from the portions on the positive directionsides and the negative direction sides in the y axis direction of theportions in which the opening portions O1 to O8 are provided, and henceit is possible to prevent the via hole conductors B3 to B16 frominhibiting the signal line 10 a from becoming inflected.

Hereinafter, a signal line according to an example of a modification ofa preferred embodiment of the present invention will be described withreference to drawings. FIGS. 3A-3D are exploded views of a signal line10 b according to an example of a modification according to a preferredembodiment of the present invention. In addition, FIG. 1 provides anexternal appearance perspective view of the signal line 10 b.

The signal line 10 b differs from the signal line 10 a in that theopening portions O11 to O18 are not provided in the ground conductor 34.Since the other configuration of the signal line 10 b is preferably thesame as the signal line 10 a, the description thereof will be omitted.

The signal line 10 b is inflected so that the ground conductor 30 islocated on an outer periphery side, compared with the ground conductor34. More specifically, when being viewed from the y axis direction, thesignal line 10 b is inflected so as to have a U shape protruding towarda positive direction side in the z axis direction. This is because theground conductor 30 easily stretches compared with the ground conductor34.

In addition, in the signal lines 10 a and 10 b, the via hole conductorsB9, B10, B27, and B28 that are located near the center of the signalline portion 16 in the x axis direction may be omitted. In this case, itis possible to more easily inflect the portion in the neighborhood ofthe center of the signal line portion 16 in the x axis direction. Inaddition, the via hole conductors B1, B2, B17, B18, B19, B20, B35, andB36 that are located near both ends of the signal line portion 16 in thex axis direction may be omitted. In this case, it is possible to moreeasily inflect the portions in the neighborhoods of both ends of thesignal line portion 16 in the x axis direction.

Hereinafter, a circuit substrate according to a second preferredembodiment of the present invention will be described with reference todrawings. FIG. 4 is an exploded perspective view of a circuit substrate110 according to the second preferred embodiment. In FIG. 4, thelamination direction of the circuit substrate 110 is defined as a z axisdirection. In addition, the longitudinal direction of the circuitsubstrate 110 is defined as an x axis direction, and a directionperpendicular to the x axis direction and the z axis direction isdefined as a y axis direction.

As illustrated in FIG. 4, the circuit substrate 110 preferably includesa laminated body 112, an external terminal 114, ground conductors 130(130 a, 130 b), 134 (134 a, 134 b), and 140 (140 a, 140 b), a linearsignal line 132 (132 a to 132 d), and a via hole conductor B. Inaddition, reference symbols are only assigned to the representativeexamples of the external terminal 114 and the via hole conductor B.

As illustrated in FIG. 4, the laminated body 112 includes a signal lineportion 116 and circuit portions 118 and 120. The signal line portion116 extends in the x axis direction, and includes the linear signal line132 and the ground conductors 130 and 134. The signal line portion 116is configured so as to be able to be bent into a U shape. The circuitportions 118 and 120 are provided at both ends of the signal lineportion 116 in the x axis direction, and include circuits. In thisregard, however, in FIG. 4, the illustration of the correspondingcircuits is omitted. Insulation sheets (insulator layers) 122 (122 a to122 d) illustrated in FIG. 4 are laminated from the positive directionside of the z axis direction to the negative direction side thereof inthis order, thereby configuring the laminated body 112.

The insulation sheet 122 is configured using thermoplastic resin such asliquid crystalline polymer having flexibility, or the like. Asillustrated in FIG. 4, the insulation sheets 122 a to 122 d areconfigured using signal line portions 124 a to 124 d, circuit portions126 a to 126 d, and circuit portions 128 a to 128 d, respectively. Thesignal line portion 124 configures the signal line portion 116 of thelaminated body 112, and the circuit portions 126 and 128 configure theconnector portions 118 and 120 of the laminated body 112, respectively.In addition, hereinafter, a main surface on a positive direction side inthe z axis direction of the insulation sheet 122 is referred to as afront surface, and a main surface on a negative direction side in the zaxis direction of the insulation sheet 122 is referred to as a backsurface.

As illustrated in FIG. 4, a plurality of the external terminals 114 areprovided on the front surfaces of the circuit portions 126 a and 128 a.In the external terminal 114, a semiconductor integrated circuit, achip-type electronic component, or the like is mounted.

As illustrated in FIG. 4, the signal lines 132 a to 132 d are linearconductors provided within the signal line portion 116, and are providedon the front surface of the insulation sheet 122 c. The linear signallines 132 a to 132 d extend in parallel or substantially in parallel toone another in the x axis direction on the front surface of theinsulation sheet 124 c. In addition, both ends of each of the linearsignal lines 132 a to 132 d are located at the circuit portions 126 cand 128 c, respectively, and are connected to circuits (not illustrated)provided in the circuit portions 126 c and 128 c.

As illustrated in FIG. 4, the ground conductors 130 a and 130 b areprovided on a positive direction side in the z axis direction within thesignal line portion 116, compared with the linear signal lines 132 a and132 b, and more specifically, are provided on the front surface of theinsulation sheet 122 b. The ground conductors 130 a and 130 b extend inthe x axis direction on the front surface of the linear signal lineportion 124 b. Both ends of each of the ground conductors 130 a and 130b are located at the circuit portions 126 b and 128 b, respectively, andare connected to circuits (not illustrated) provided in the circuitportions 126 b and 128 b. Furthermore, as illustrated in FIG. 4, theground conductors 130 a and 130 b overlap with the linear signal lines132 a and 132 b, respectively, in the planar view seen from the z axisdirection.

In addition, as illustrated in FIG. 4, in the ground conductors 130 aand 130 b, a plurality of opening portions O in which no conductor isprovided are arranged along the linear signal lines 132 a and 132 b inthe planar view seen from the z axis direction. In addition, in FIG. 4,a reference symbol is only assigned to the representative example of theopening portions O. In addition, since the configurations of the openingportions O are preferably the same as those of the opening portions O1to O8 in the signal line 10 a, the further descriptions thereof will beomitted.

As illustrated in FIG. 4, the ground conductors 134 a and 134 b areprovided on a negative direction side in the z axis direction within thesignal line portion 116, compared with the linear signal lines 132 a and132 b, and more specifically, are provided on the front surface of theinsulation sheet 122 d. The ground conductors 134 a and 134 b extend inthe x axis direction on the front surface of the signal line portion 124d. Both ends of each of the ground conductors 134 a and 134 b arelocated in the circuit portions 126 d and 128 d, respectively, andconnected to the ground conductors 140 a and 140 b provided in thecircuit portions 126 d and 128 d, respectively. Furthermore, asillustrated in FIG. 4, the ground conductors 134 a and 134 b overlapwith the linear signal lines 132 a and 132 b, respectively, in theplanar view seen from the z axis direction. In addition, no opening O isprovided in the ground conductors 134 a and 134 b.

The ground conductors 140 a and 140 b are arranged to coverapproximately the entire surfaces of the circuit portions 126 d and 128d, and a ground potential is applied to the ground conductors 140 a and140 b. Since the ground conductors 140 a and 140 b are manufacturedusing metal foil or the like, it is hard for the ground conductors 140 aand 140 b to be deformed, compared with the insulation sheet 122. Here,in the planar view seen from the z axis direction, the percentage of themetal foil in the circuit portions 118 and 120 preferably is higher thanthe percentage of the metal foil in the signal line portion 116.Therefore, it is hard for the circuit portions 118 and 120 to bedeformed, compared with the signal line portion 116. More specifically,in the circuit substrate 110, the circuit portions 118 and 120 configurea rigid portion, and the signal line portion 116 configures a flexibleportion. In this way, the rigid portion is provided, and hence it ispossible to stably and reliably mount an electronic component, asemiconductor integrated circuit, or the like on the circuit portions118 and 120.

As illustrated in FIG. 4, the via hole conductors B are provided so asto penetrate through the signal line portion 124 b in the z axisdirection, and connect the ground conductors 130 a and 130 b to theground conductors 134 a and 134 b, respectively. In addition, since thevia hole conductors B are preferably the same as the via hole conductorsB1 to B36 in the signal line 10 a, the descriptions thereof will beomitted.

The insulation sheets 122 a to 122 d having the above-mentionedconfigurations are laminated, and hence the ground conductors 130 a and134 a and the linear signal line 132 a define a stripline structure. Inthe same way, the ground conductors 130 b and 134 b and the linearsignal line 132 b define a stripline structure. Furthermore, the groundconductors 130 a and 130 b are connected to the ground conductors 134 aand 134 b using the via hole conductors B.

The circuit substrate 110 having the above-mentioned configuration isused in a state in which the circuit substrate 110 is inflected. Morespecifically, in the planar view seen from the y axis direction, thesignal line portion 116 is inflected so as to form a U shape protrudingtoward a positive direction side in the z axis direction.

In the same way as the signal line 10 a, it is possible for the circuitsubstrate 110 as described above to be easily inflected and tosignificantly reduce unnecessary radiation.

In addition, the openings O may also be provided in the groundconductors 134 a and 134 b.

Preferred embodiments of the present invention are useful for a signalline and a circuit substrate, and, in particular, superior in that it ispossible to inflect the signal line and the circuit substrate and it ispossible to reduce unnecessary radiation.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A signal line comprising: a laminated bodyincluding a plurality of insulator layers that include flexible materialand are laminated on each other in a lamination direction; a linearsignal line provided within the laminated body; a first ground conductorlocated above the linear signal line in the lamination direction withinthe laminated body and overlapping with the linear signal line in aplanar view seen from the lamination direction; a second groundconductor located below the linear signal line in the laminationdirection within the laminated body and overlapping with the linearsignal line in the planar view seen from the lamination direction; and avia hole conductor connecting the first ground conductor and the secondground conductor to each other; wherein in the first ground conductor, aplurality of first opening portions are arranged along the linear signalline in the planar view seen from the lamination direction; and in theplanar view seen from the lamination direction, the via hole conductoris provided on an imaginary line that connects two corners of the firstopening portions adjacent to one another.
 2. The signal line describedin claim 1, wherein in the second ground conductor, a plurality ofsecond opening portions are arranged to overlap with the first openingportions such that the second opening portions coincide with the firstopening portions, in the planar view seen from the lamination direction.3. The signal line described in claim 1, wherein an opening portion inwhich no conductor layer is provided is not provided in the secondground conductor, and the laminated body is inflected so that the firstground conductor is located on an outer periphery side thereof, comparedwith a location of the second ground conductor.
 4. The signal linedescribed in claim 1, wherein the via hole conductor is provided on aperpendicular bisector with respect to centers of the first openingsthat are adjacent to each other, in the planar view seen from thelamination direction.
 5. The signal line described in claim 1, whereinthe first openings overlap with the linear signal line in the planarview seen from the lamination direction.
 6. A circuit substratecomprising: a main body including a plurality of insulator layers thatinclude flexible material and are laminated on each other in alamination direction and including a first circuit portion, a secondcircuit portion, and a signal line portion; a linear signal lineprovided within the signal line portion; a first ground conductorlocated above the linear signal line in the lamination direction withinthe signal line portion and overlapping with the linear signal line in aplanar view seen from the lamination direction; a second groundconductor located below the linear signal line in the laminationdirection within the signal line portion and overlapping with the linearsignal line in the planar view seen from the lamination direction; and avia hole conductor connecting the first ground conductor and the secondground conductor to each other; wherein in the first ground conductor, aplurality of first opening portions are arranged along the linear signalline in the planar view seen from the lamination direction; in theplanar seen view from the lamination direction, the via hole conductoris provided on an imaginary line that connects two corners of the firstopening portions adjacent to one another; and the first circuit portionand the second circuit portion include a first circuit and a secondcircuit, respectively, the first circuit and the second circuit beingconnected to the linear signal line, the first ground conductor, and thesecond ground conductor.
 7. The circuit substrate described in claim 6,wherein in the second ground conductor, a plurality of second openingportions are arranged to overlap with the first opening portions suchthat the second opening portions coincide with the first openingportions, in the planar view seen from the lamination direction.
 8. Thecircuit substrate described in claim 6, wherein an opening portion inwhich no conductor layer is provided is not provided in the secondground conductor, and the laminated body is inflected so that the firstground conductor is located on an outer periphery side thereof, comparedwith a location of the second ground conductor.
 9. The circuit substratedescribed in claim 6, wherein the via hole conductor is provided on aperpendicular bisector with respect to centers of the first openingsthat are adjacent to each other, in the planar view seen from thelamination direction.
 10. The circuit substrate described in claim 6,wherein the first openings overlap with the linear signal line in theplanar view seen from the lamination direction.